Pages

Friday, July 30, 2010

Spaceflightnow.com has an article on the end of the Mars Scout program. The article suggests that this was a recent event, while I recall the program having been canceled -- or perhaps more correctly being folded into the Discovery program -- a year or two ago.

Originally conceived of as a series of small missions similar in scope and cost to the Discovery program, the Scout program was envisioned to fly missions to supplement the large missionss. Each Scout mission would be lead by a principal investigator who would propose the mission and manage it through development and flight. This was in contrast to the large orbiters and rovers that were defined by committees of scientists and managed by the Jet Propulsion Laboratory. The Phoenix lander was the first mission in the program and the MAVEN orbiter planned for launch in 2013 will be the second and last mission.

The article states that the reason for cancellation was that the focus for Mars exploration will be landed missions, which don't fit into the Scout budget. (Phoenix slipped in under the budget cap because it used an already designed and mostly built lander from a canceled mission.) My understanding is that a changing budget situation ended the program. When it was initiated, the Mars program was expected to be funded at a higher level than turned out to be be case. In addition, cost overruns on the Mars Science Laboratory reduced funding for future Mars missions (although the MAVEN mission was protected from cuts).

NASA has not abandoned small missions to Mars. Now they must compete with other solar system targets within the Discovery program. The Spaceflightnow.com article notes that several proposals for Mars missions will be submitted as part of the current Discovery mission selection process.

The MAVEN orbiter will study the upper atmosphere of Mars. Courtesy NASA

Editorial Note: Small Mars missions may lack the inherent attraction of missions to less visit parts of the solar system such as Io, Titan, comets, and asteroids. However, Mars orbiters may represent excellent science return for the buck while representing low implementation risks. Our moon has been the most visited destination in the solar system, but the last Discovery competition selected the GRAIL lunar gravity mission, presumably on these criteria.

Thursday, July 29, 2010

Researchers writing in Earth and Space Sciences suggest that the Nili Fossae region of Mars resembles the East Pilbara area of Western Australia, which contains early fossil records of life on Earth. If their interpretation of possible hydrothermal activity on Mars is correct, this would be a key location to explore for fossils on Mars. At one time, this area was in contention for the Mars Science Laboratory mission until further analysis showed it to be too rough to guarantee a safe landing. Sciencedaily.com summarizes the research at while Wikipedia provides background on the Pilbara craton in Western Australia that preserves the only pristine areas of the Earth's crust from 2.6-2.7 billion years ago. An abstract provides information on the geological setting of Earth's oldest fossils within this region. [Editorial note: I was seriously bummed when Nili Fossae had to be dropped as a possible MSL landing site. From the descriptions of the site, the views of landscape would have been dramatic, much like the views in the American southwest.]

THEMIS spacecraft

Two NASA spacecraft are on their way to orbit the moon to study the solar wind and lunar fields and particles environment moon. Both spacecraft are members of the five spacecraft THEMIS mission launched in February 2007 that has been studying the Earth's magnetosphere. The craft will assume station keeping at the Earth-Moon L1 and L2 Lagrangian points in October 2010 followed by entry in lunar orbit in April 2011. Following their 18 month mission to study the lunar environment, the spacecraft will be commanded to crash into the moon. Aviation Week and Space Technology has an article on the planned mission. Miscellaneous

India is continuing its planning for its next lunar mission consisting of an orbiter and Russian lander/rover. Instruments for the planned 2012 mission will be selected in the next month. Spacedaily.com has a short article on the instrument selection and Wikipedia adds a few more details on the mission. [Editorial note: Instrument selection now for a mission to fly within two years seems like short lead time.]

Monday, July 26, 2010

Running in parallel with, but about nine months ahead, of the planetary Decadal Survey has been an astronomy decadal survey. The results of that survey will be released on August 13. While the results likely will be widely reported, this is the link to the official site http://sites.nationalacademies.org/BPA/BPA_049810

Unfortunately, you probably will not read about the results first on this blog. I will be out in the field helping a friend out with some research. I should have a summary within 2-3 days afterward, however.

This impending announcement got me to revisit the schedule for the planetary Decadal Survey. It looks like the first time that the public will see the results will be March of next year. Drafts will begin circulating to reviewers in the fourth quarter of this year, but leaks historically appear to have been rare. Here is the schedule presented at the Outer Planets Assessment Group (OPAG) last spring:

Saturday, July 24, 2010

Artist's conception of the MoonRise lunar return mission that is a finalist for the current New Frontiers selection.

If you look at the list of missions being considered by the Decadal Survey, a few themes stand out. One is the exploration of the ice and ocean moons of Jupiter and Saturn (Europa, Ganymede, Titan, and Enceladus), another is the exploration of Venus, and a third are sample return missions. (A sprinkling of individual missions to other worlds such as Mercury, Chiron, and Neptune-Triton round out the list.) [Tidbit: One recent article listed the number of missions being considered by the Survey as 28, up from the list of 25 posted on its website. The potential missions to select from may be even more interesting than the current list -- which is already quite an interesting list.]

A number of my blog entries have summarized ideas for all of these themes, but I have given more space to discussing campaigns of missions to ice-ocean moons and Venus than I have a campaign of sample return missions. This blog entry will try to provide balance by considering sample return missions.

The return of samples from solar system bodies has been a focus on planetary mission planning for decades. While the instruments carried by spacecraft are marvels of engineering, they must be built to meet severe constraints for mass, size, and power. Many of the instruments routinely used on Earth exceed the size and mass of the entire spacecraft; in the case of the synchrotrons used to study the Stardust comet grains, the instruments exceeded the size of the launch pad used for the mission. The instruments in laboratories can probe individual grains in exquisite detail and compositional resolution that no spacecraft can. Unlocking many of the secrets of the solar system and its worlds will require bringing back samples to Earth.

Unfortunately, sample return missions are inherently costly. As with a non-sample return mission, a spacecraft must be delivered to its target world. Most mission concepts include a fairly robust suite of instruments to survey the target body and to select optimal sampling sites. (The MoonRise lunar sample return mission is an exception; the fleet of recent missions to the moon already have provided the remote sensing context.) Just to get there and survey the locale requires a fairly capable mission. Then the sample must be collected, which can require complex sample acquisition, handling, and storage devices. The spacecraft, or a portion of it, must maneuver back to Earth and successfully deploy a return capsule with the sample through the atmosphere.

There are a range of mission complexities and corresponding costs. At the low end, the Genesis solar wind and the Stardust comet missions were able to capture their samples in flight. The next step up would be to sample a near Earth asteroid or a comet. Such missions do not require sophisticated ascent vehicles, but the ultra-low gravity and poorly understood surfaces create their own engineering problems. A sample return from our moon would require a capable lander and ascent vehicle. And at the far end of the scale would be a Mars sample return mission that would require multiple launches and a small flotilla of craft to gather and return the samples.

Five possible targets for sample return missions are being studied by the Decadal survey: the moon, a near Earth asteroid, a comet, Enceladus, Mars. The first three targets possibly could be accomplished within the budget of a New Frontiers mission (~$650M). Comet sampling missions could range across a wide range of prices from mission that collects dust during repeated low-speed passes above the nucleus (Discovery class?), to a mission that returns a warm sample with volatiles in liquid form (New Frontiers?), to a mission that returns frozen volatiles (perhaps 2X New Frontiers cost?). At the high end of the missions would be a Mars sample return mission at a possible cost of $6-7B. (I have yet to see a cost estimate for an Enceladus sample return that would collect ice particles while passing through that moon's geysers.)

The Decadal Survey could decide that further missions to flyby, orbit, and land on these worlds for remote sensing and in-situ studies are unlikely to provide more than incremental increases in our knowledge of these worlds. By the time a sample return mission could be flown to each target, we will have orbited or rendezvoused with three asteroids and flown by several more, have rendezvoused with and landed on a comet and flown by several more, have studied the moon in depth from orbit and sampled the near side, and will have orbited and landed on Mars many times. A revolutionary increase in our knowledge may require bringing home samples.

What might a sample-return focused set of missions look like? At 2011 spending levels (adjusted for inflation), NASA will have ~$13B to spend on planetary missions in the coming decade. Here is a possible breakdown of missions and possible costs (costs are best guesses from estimates published in various sources; many are probably wrong):

*Assuming the mission could be done for the fully burdened cost of a New Frontiers mission
**Needed to image landing sites and serve as data relay for the Mars sample return missions; cost is a guess and probably doesn't reflect NASA's planned costs
****A guess and possibly low

Editorial thoughts: A program focused on ice-ocean moons, Mars, or sample returns would be intellectually sound. Where the Decadal Survey ultimately decides to place its focus will be known in a few months. I've discussed this with a few members of the planetary science community. In many respects, the mission mix reflects which scientific specialties receive favor. Missions to ice-ocean moons, for example, favor scientists with expertise in remote sensing and in-situ instruments. Sample return missions favor scientists with expertise in laboratory analysis and laboratories with the right instruments. The Survey may ultimately decide on a program that is a mixture of elements to serve the needs of all groups.

Long term readers of this blog know that I am skeptical that a Mars sample return mission will every fly. That's not because I don't believe that a sample return would return scientific knowledge equal to the price tag. Rather, I doubt that the political systems of space faring nations will foot the cost short of a previous mission finding clear signs of possible life, past or present. (Note to my Congressman and Senators: Feel free to prove me wrong.)

Whatever goals the Decadal Survey sets for NASA, the Japanese space agency is planning a second near Earth asteroid mission and the Russian space agency is planning a sample return from the Martian moon Phobos. The ESA is planning to issue a call for another round of proposals for medium sized science missions, and a near Earth asteroid mission is likely to be proposed again. Two of the finalists for the current NASA New Frontiers mission are sample returns (from the moon and a near Earth asteroid). It would seem that sample return missions will be playing an increasingly large role in programs of planetary exploration.

Wednesday, July 21, 2010

Spaceflight Now has an article that provides an update on the plutonium-238 supply problems. This radioisotope is used as a power source for missions where solar power is impracticle or impossible. Currently, the US does not have enough Pu-238 to enable the proposed Jupiter Europa Orbiter (JEO) mission that NASA would like to fly at the end of the decade. According to the article, if Russia either agrees to resume selling Pu-238 to the US, or Congress approves start up of new Pu-238 production in the FY11 budget, then sufficient Pu-238 supplies will be on hand for the JEO mission. [Editorial thought: While NASA would probably prefer to have both sources of Pu-238, restarting production probably would be the more desirable alternative of the two. Russia no longer produces Pu-238, so NASA would like to have an ongoing source of new material.]

In the mean time, the European Space Agency would like to begin flying missions that require radioisotope power in the 2020s. It apparently has concluded that it should not depend on the US supplying Pu-238. (Besides the uncertainties of US budgets, my understanding of US law is that the US cannot provide Pu-238 for launch on a foreign launch vehicle. ESA, I presume, would like to use its own launchers.) ESA is looking at an alternative radioisotope, americium-241. This radioisotope has a longer half life than Pu-238, but produces less heat and therefore fewer watts of electricity. It appears that ESA is currently in the early exploratory phase of this idea, and it is not yet a committed, funded project.

Monday, July 19, 2010

If you follow space exploration at all, you are probably aware that NASA's manned spaceflight program is undergoing a major overhaul. A vigorous debate has broken out about how to replace the goals and programs of the previous moon-based plan with a new program that will fit within the projected NASA budget. In the US, the President generally proposes program direction but Congress must ratify and fund that direction. The in's and out's of the debate are outside the scope of this blog. However, it appears that a compromise has been developed and approved as an authorization by the Senate. Authorizations are essentially Congress' policy documents that are supposed to guide the actual budget, but the connection between the two are sometimes tenuous. If you are interested in following the process, I recommend www.spacepolitics.com.

I've held off on reporting on this process until a consensus had appeared to form. According to Aviation Week and Space Technology (subscription article), the current proposal will leave the President's request for FY11 science funding -- including the planetary program -- untouched. This would be good news since the proposed budget provides a one time increase above the inflation level for the planetary program. However, the technology development program (which is part of the manned rather than science budget) will be dramatically reduced to help pay for the other elements of the manned spaceflight program. This budget was to have included an ambitious program of precursor missions to the moon, near Earth asteroids, and Mars. We'll have to wait for the details of the final budget to see if any of these proposed missions will survive.

Monday, July 12, 2010

Last week, the journal Nature published an update on the challenges facing the Decadal Survey. In a nutshell, the planetary program has three major programs it would like to fund, but money for only two. The article focuses on the contention between two of those programs, a three part $6-7B Mars sample return and a $3.2B Jupiter Europa Orbiter, and concludes that it's unlikely both could fit into the probable budget for the coming decade. However, if that budget turns out to be close to $12B (which would be the approximate budget presuming similar funding to this year carried forward for a decade), then both missions could be funded. Doing so, however, would squeeze out the third program of smaller Discovery (~$800M) and New Frontiers (~$1.2B) missions that provide balance and breadth to the program.

"As usual, says committee member Stephen Mackwell, director of the Lunar and Planetary Institute in Houston, Texas, there is too little money for too many ideas. 'We have to deal with a whole Solar System of possibilities,' he says.... 'I find it very hard to see doing them both in the decade,' says Fran Bagenal, former chairwoman of an external NASA planetary-science advisory committee... What's more, attempting a Europa mission and the Mars sample return at the same time could crowd out smaller missions to other parts of the Solar System, says Alfred McEwen, principal investigator for the HiRISE camera on the Mars Reconnaissance Orbiter, which is currently imaging Mars... "What Squyres has called 'sticker shock' for the biggest missions could bias the survey in favour of small- and medium-cost mission lines known as Discovery and New Frontiers. 'I could put together a spectacular programme without either one of those [flagship missions]. There are many ways to slice this,' says Squyres."

Editorial Thoughts: This crunch between desires and budgets isn't a surprise. In my analysis of NASA's budget for the last two years, I have not seen a way to fund all three programs within the probable budget for the coming decade. The increasing political focus on cutting federal budgets would seem to make it unlikely that the planetary program budgets will grow, and we may well see cuts. The Nature article points out that the proposed Precursor missions could add additional missions to the line up. However, the budget for these missions seems extremely uncertain as the administration and Congress argue over the nature and budget for the manned spaceflight program that would pay for the Precursor missions. If any of these missions survive, I suspect that the focus will be on near Earth asteroids, which would be the first focus of manned exploration.

What follows is my analysis of the pros and cons for a program that focuses on any of the three major program options.

Mars Sample Return

Pro: The analysis of carefully selected samples from Mars would revolutionize our understanding of Mars and, by extension, conditions on the early Earth. If those samples include signs of past or current life, then the mission will revolutionize our understanding of our place in the universe. The ability to tease out insights from samples with sophisticated instruments in terrestrial labs cannot be overstated. While instruments on planetary probes are engineering marvels, mass, volume, and power restrictions restrict their sensitivity.

Con: While Mars sample return missions have been studied for decades, detailed engineering analysis has rarely been done. The current concept for a three part mission is still fairly new, and the possibility of rapidly rising costs is real. Then there is the question of whether there is the political will to fund a mission this large. Political support would have to be sustained through 2-4 presidencies (depending on whether incumbents win re-election) and 8 Congresses. The complexity of the program with three major mission elements (a sample colleciton rover, a Mars lander with ascent vehicle, and a spacecraft to fetch the samples from Martian orbit and return them to Earth) means that many mission elements must go off without a failure to actually return the samples. There is also the question of where and how to sample. We know enough about Mars to pick a good location to sample, but will politicians fund this large a program without assurances that we already know that the chosen sampling location is optimal? And should samples be taken from near the surface (current plan), from the shallow subsurface (where ExoMars will sample), or from the deep subsurface?

Jupiter Europa Orbiter

Pro: This mission appears technically ready to enter development after a decade of technology development and analysis. Europa is one of the most likely spots in the solar system in which to find life, and the mission would also study the rest of the Jovian system. The proposed spacecraft will have the capability to study Europa in depth and to locate places on the surface where ocean material has recently been brought to the surface where future landers could study it.

Con: This mission is a bet that Europa (1) harbors an environment capable of supporting life and that (2) locations can be found near at the surface where future (expensive) landers could explore in more detail. Without the possibility of explorable life (life locked below a hundred kilometers ice would be unreachable with current technology and budgets), would the planetary community choose to spend $3.2B to explore this moon? This mission also requires a larger stockpile of Pu-238 to fly than NASA currently has on hand. Either the Russians would have to agree to resume sales of Pu-238 to the U.S., or the U.S. would have to restart Pu-238 production, which may not occur in time to fly this mission by the end of the decade.

Discovery and New Frontiers Missions

2 small flagship ($1.8B or 1.5 times the standard New Frontiers mission) missions that might fund a Mars rover, a network of Mars landers, a cryogenic comet sample return, or a Jovian or Saturn orbiter to continue the exploration of the moons of those worlds.

4 standard (~$1.2B) New Frontiers missions that might include a Ganymede orbiter with Europa and Callisto flybys; a near Earth asteroid sample return; and Venus lander; a lunar sample return; a mission to flyby Neptune, Triton, and Kuiper belt object; or a modest Enceladus mission.

4 Discovery (~$800M) missions that might fund the U.S. contribution to the Mars Trace Gas Orbiter, remapping Venus with radar at higher resolution, an Io volcano observer, a Titan lake lander, a Trojan asteroid mission, a Venus balloon mission, or a comet lander.

(Note: The missions listed above are possibilities. At least some of them probably would prove too expensive for the mission class suggested.)

One advantage of a program built on smaller missions is that if budgets are cut or one mission has to be cancelled because of cost overruns or technical difficulties, a robust program remains.

Con: None of these missions is likely to revolutionize our understanding of the solar system or to find an abode of past or present life. The Mars sample return and Jupiter Europa Orbiter missions have remained at the top of the priority list for solar system exploration because they offer the chance for a revolutionary discovery.

What's my take on the options? A program that focused on any of these elements can be justified in terms of scientific return for dollars spent. A Mars sample return mission is a high risk/high return proposition, because it could consume the budget for a decade only to fail because of eventual political cancellation or because one of the many critical mission stages ends in disaster. Combining the Jupiter Europa Orbiter with several New Frontier and Discovery missions would be a less risky approach, but would leave key questions about Mars -- the most Earth-like world -- unanswered.

It will be very interesting to see how the Decadal Survey resolves these problems. The Survey members could go for a compromise that funds the first element of the Mars sample return mission (the ~$1.9B sample acquisition rover), the Jupiter Europa orbiter, and a modest New Frontiers and Discovery program. Or they could decide to radically restructure the shape of the program and bet big on Mars or to go only with smaller missions. The Nature article suggests that we may see the first draft of the proposed plan this Fall.

Friday, July 2, 2010

Some of the most interesting places in the solar system unfortunately present some daunting challenges to explore. The intense radiation fields at Europa are probably the quintessential example of this problem. With a decade of technology development to push radiation hardened engineering and a $3B+ budget, the proposed Jupiter Europa Orbiter will survive for an estimated 9 months or so after it enters orbit. With that short of a lifetime and a whole world to explore, a fairly small percentage will be imaged at high resolution. Eventual lander missions (if the findings of the orbiter warrant what would likely be a Flagship class mission) will be equally time pressed.

The hellishly hot surface of Venus provides its own challenge. Landers and probes have lasted on the surface for an hour or so in the past. The next generations of landers under consideration by NASA are targeting landed or near surface lifetimes of two-five hours. These landers extend their life by including phase change materials within the landers. Much as the ice in your ice chest does, these materials absorb heat as they change from solid to liquid. Once the phase change is complete, however, the interior of the lander's temperature will rise as heat soaks through the shell. The lead author of the Venus Mobile Explorer, Lori Glaze at the Goddard Spaceflight Center, explained to me in an e-mail the challenges faced by designers of Venus landers. "The real challenge here is that if you want to keep the lander 'cool' you have to provide more phase change material, which has mass...At some point, you just can’t get this massive system off the ground at Earth." As a result, Venus landers seemed destined to have just a few hours to perform their studies. Long term studies can be done from balloons and orbiters, but long-term surface missions are beyond our capabilities. (In theory, refrigeration units powered by plutonium 238 could resolve this problem. However, these systems operate based on the difference in heat between the plutonium and a thermocouple. It's hard to "dump" the heat of the Pu-238 into an already hellish hot atmosphere to maintain the temperature difference.)

Titan has neither radiation fields nor heat to deal with. It's atmosphere and surface are hellishly cold, but nuclear power systems do operate well in cold environments (easy to maintain that heat differnce). This is a world that has a surface that in many ways may be most Earth-like of any body in the solar system with river valleys, seas and lakes, mountains, and a host of other interesting terrains. Titan deserves the high resolution imagery that has advanced our understanding of the other Earth-like surface, Mars. Unfortunately, the atmosphere of Titan and the dim light so far from the sun makes high resolution imaging from orbit almost impossible. At Mars, orbiters can operate at 150 km altitude, while the atmosphere of Titan requires an altitude of 1500 km. To see through the haze in a spectral window, a camera has to operate in near infrared bands. The sun is dimmer at these wavelengths than at visible wavelengths and Saturn is far from the sun. So to collect enough light to illuminate each pixel sufficiently for a clean image, a large mirror would be needed for high resolution imaging. As a result of these limitations, the proposed Titan Flagship orbiter would have imaged the surface at 50 m per pixel where Mars is imaged at 30 cm per pixel. (Radar instruments would have their resolution degraded by the increased altitude compared to what could be done at Venus or Mars.) In addition, either optical or radar imaging system generate lots of data, which from the distance of Saturn require high powered communications systems. High power communications systems require large power systems (and likely lots of Pu-238) leading to a large spacecraft. Net result is that global, moderate resolution (~50 m) mapping of Titan may require a small Flagship-class (($1.5-2.0B?) missions. In the meantime, in situ probes like the proposed TIME lake lander and the AVIATR plane offer ways to increase our knowledge of Titan at much more moderate costs.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.